Each site on each map has a “default” spot on which to plant the spike. Default plants are useful as they typically provide maximal cover to the planter on the typical site take, and because the majority of lineups that your teammates may know require the spike to be planted default. The default plant on B Split, for example, is behind the small box next to the pillar and provides cover from rafters, CT, and the majority of site. The white spots on the map below represent angles from which the default plant can be contested (contesting by swinging, not through utility usage).
Default plants can be used in the face of some degree of pressure due to the cover they typically provide the planter. So why plant anywhere else? There are a number of reasons. For one, the safety provided by the default plant works both ways. While it protects you as the planter, it can also protect the person attempting to defuse. The default plant on A site Icebox sits in the small corner between the hop-up boxes and the rope for top nest.
The white spots on the map above represent angles from which the defuse can be contested by attackers assuming they’ve given up site. If control of the site is given up in the post-plant, checking for a player defusing requires you to expose yourself to a number of angles with minimal cover (many players avoid these disadvantageous swings through utility usage). Swinging out towards fridge, using the rope to jump on 510, or walking through pipes and up to the spike are all risky plays.
Another reason not to plant default is that seldom-used plant spots can confuse enemies on the retake. A majority of the experience that players will have on a retake is against a default plant, including the common angles and spots to check in response. By planting elsewhere, you decrease the degree to which the other player can rely on past experience to autopilot through a retake. Take the default plant on A site Haven as an example.
The team retaking site, once they’ve cleared everything up to the spike itself, knows that the remaining players must either be cubby, short, or long, as no other angle has a clear view of the spike. If an attacker loops through B and flanks through link or heaven, they will likely have to make noise in order to put themself in position to contest the defuse. This makes things as simple as possible for the defenders, and as risky as possible for the attackers. Knowing that there are essentially two angles to cover, defenders with numbers advantage will typically have an easy time securing the defuse. Let’s consider an alternative plant.
Planting along the right wall of site, while potentially much riskier to pull off, has the advantage of making the defuse visible from every potential angle into site. Whereas in the previous example the retaking team had two angles to worry about, now they have a minimum of four. A late lurk will be considerably more effective in this scenario as the spike is visible from both link and heaven, in addition to being visible from short and long. Not only that, but the spike is visible from deeper angles on both short and long, meaning that attackers don’t have to expose themselves as much to check the defuse. On the default plant, an attacker sitting long would have to walk halfway up the ramp before the spike would be visible. By planting along the right wall, he doesn’t expose himself to anything other than a tiny sliver of site in order to check the defuse. While planting in such a spot is risky as it provides no cover, once the plant is secured it drastically increases your chances of winning the round. No cover for your plant means no cover for the defuse either (sage walls and smokes excepted).
So how should you determine where to plant? If you are, or could be facing pressure, plant where you have maximal cover. This will often be the default plant, but depending on the positioning of your team and the information you have regarding the positioning of the other team, it could mean planting in an unorthodox spot. If you know that you will not be contested during the plant, and won’t be exposing yourself to unnessecary risk, plant such that the spike is visible from as many places as possible. This will often mean planting in the open with no cover whatsoever, so make sure that your team is covering you. Communicate to your team that you aren’t planting default.
One final piece of advice on planting: if you are by yourself with spike, far away from your team, please don’t plant (unless you are out of time). A 5v1 situation in which the planter is alone and dies to the singular player on the other team is a guaranteed loss. Make sure that when you plant you have at least one teammate within range to contest the defuse should you die. Often you will see an Omen use his ult to take the spike across the map to the other site. This isn’t necessarily a bad play, but can easily become one if he plants before your team has had a chance to rotate close enough to defend the spike should he die. The player with spike should not be alone as a general rule, but should certainly never plant without support (unless it is the only way to potentially win the round).